Process for the manufacture of dihydroxy isodibenzanthrone



Patented Jan. ll, i938 2,l04,96ll

Robert Fraser Thomson, Kan Blohm Anderson,

and Sidney Thornley,

Grangemouth, Scotland,

assigncrs to Imperial Chemical Industries Limited, a corporation ofGreat Britain No Drawing. Application July 18, 1936, Serial No. 91,440

2 Claims.

This invention relates to improvements in the process for preparingoxidation products of isodibenzanthrone.

U. S. Patent Reissue 16,426 describes the oxi 5 dation ofiscdibenzanthrone in strong sulfuric acid with manganese dioxide at 60C. The resulting product after being treated with sodium bisulfite ismethylated to give a dyestufi which dyes cotton from a blue vat ingreenish-blue shades. When the methylation is carried out innitrobenzene, according to the procedure outlined in Example B of thepatent, a relatively pure dyestufi crystallizes out(dimethoxy-isodibenzanthrone) if the nitrobenzene filtrate is allowed tocool before it is concentrated. This pure dyestufi" dissolves inconcentrated sulfuric acid with a claret color, while the impuritieswhich remain in the nitrobenzene solution and which may be obtained onfurther concentration of such solution dissolve in sulfuric acid with agreen color. These impurities, if precipitated with thedimetho'xy-isodibenzanthrone from the nitrobenzene solution, tend todull the shades of the dyestuff and the resulting product gives a greensulfuric acid solution.

In German Patent 468,957 a process is described whereinisodibenzanthroneis oxidized in sulfuric acid monohydrate or oleum atlow temperature. The oxidation of isodibenzanthrone according to thispatent gives very low yields of the desired blue dyestuif whenmethylated according to the procedure outlined in the patent, making theprocess impractical for commercial use.

It is therefore an object of this invention to provide a process foroxidizing isodibenzanthrone whereby a product may be obtained which onsubsequent methylation will give relatively high 40 yields of a dyestuffwhich dyes cotton in desirable greenish-blue shades.

It is a further object of this invention to improve the process foroxidizing isodibenzanthrone described in U. S. Reissue 16,426 wherebyincreased yields of a relatively pure oxidatidn product ofisodibenzanthrone are obtained.

According to this invention isodibenzanthrone is suspended in moderatelydilute sulfuric acid and subjected to the action of an oxidizing agent,such as manganese dioxide, at ordinary room temperature or lower.

To more fully illustrate the invention the following example is given inwhich the parts used are by weight.

Example 100 parts of finely powdered isodibenzanthrone (obtained, forexample, according to U. S. Patent 1,924,456, Ex. 5) are suspended in2,000 parts of 92% sulfuric acid at ordinary temperature with stirring,and after cooling to to C. 130 parts of finely powdered naturalmanganese di oxide (85-86% MnOz) are added in small portions during thecourse of 2 to 3 hours, followed 10 by stirring for 15 to 16 hours atthe same temperature. The reaction mixture is then allowed to warm up to20 to C. and drowned in 10,000 parts of Water. The brown precipitate isthen treated in this dilute acid with 130 parts of sodium bisulfitewhich has been dissolved in water. The mass is brought to the boil,further diluted with 8,000 parts of cold water, filtered and washed acidfree.

The product consisting of a blue-black paste forms a blue-black powderwhen dried. It is soluble in 95% sulfuric acid with a brown color and inweak oleum with a green color. It may be methylated according to theprocedure outlined in U. S. Reissue 16,426, giving good yields of adyestuff which gives a claret color in sulfuric acid, when isolated fromthe nitrobenzene methylation mass by cooling and filtering. The purityof the dyestuff may be enhanced by recrystallization from sulfuric acid,or by a vatting procedure.

The oxidation should be carried out in sulfuric acid concentration offrom 88 to 93%. Higher concentrations of acid tend to give a morereddish-blue dyestuff which is not desirable, while the oxidation cannotbe satisfactorily carried out in lower acid concentrations at thetemperatures required by this process.

The temperatures used may range from about 0 to 25 (3., the preferredtemperatures being from 5 to 20 C. Higher temperatures with theconcentration of acid employed tend to form large amounts of by-productswhich are obtained in the process of U. S. Reissue 16,426, the formationof which materially decreases the yield of the de sirable dyestuiT.

The isodibenzanthrone may be suspended directly in the sulphuric acid ofthe specified strength or it may be dissolved in more concentratedsulfuric acid which, after solution is complete, may be diluted by thecareful addition of water, prior to the addition of the oxidizing agent.

The manganese dioxide should be added very slowly over a period ofseveral hours. Equivalent oxidizing agents, such as manganic sulfateexample, the product may also be used. In place of drowning the reactionmixture in water as described in the above may be isolated by directfiltration on a suitable filter, whereby purification is efiected. Thecrude product may also be purified by extraction with alkaline solutionsor crganic solvents. The purity of the desired oxidation productdepends, to a large extent upon the purity of the isodibenzanthroneemployed.

We claim:

1. In the process of o 'dizing isodibenzanthrone todioxy-isodibenzanthrone in sulfuric acid, the steps which comprisecarrying out the oxidation in an acid concentrationof from 88 to 93% attemperatures of from 0 to 25 C.

2. In the process for preparing dioxy-isodibenzanthrone whereinisodibenzanthrone is oxidized in sulfuric acid with manganese dioxide,the steps which comprise carrying out the oxidation in an acidconcentration of from 90 to 93% at temperatures of from 5 to 20 C.

' ROBERT FRASER THOMSON.

IAN BLOHM ANDERSON. SIDNEY THORNLEY.

